Radiator running hot...

[JMan300sd]

Last time i drove up to tallahasse from miami (500 miles) i experienced something odd. 3/4 of the way up my car ran fine and stayed below 100, but after filling up it slowly started creeping up the temp gauge. I thought the 110 switch would handle it, but it just kept going up till it hit 120. So I stopped and let it cool down, checked coolant level and proceeded and it did it again. I had to make it home so i turned on the heater and opened up all my windows and made it home running at about 110 for about 75 miles. What could have caused this?
I drive around town now and then and theres not a problem because all my driving is relativeley short in duration. But, I am driving back down in two weeks and want to make sure this problem does not repeat. What should I check on the radiator? I am going to clean out the fins, examine hoses, and replace the thermostat but beyond this what else should i look for and do? Where is the 110 switch located? Any help would be great!

[JMan300sd]

I also must mention that i have replaced the water pump witha brand new one less than 10 k miles ago.

Originally Posted by JMan300sd

Where is the 110 switch located? Any help would be great!

To my understanding, the W116 300SD only had the 110*c switch. All the W115's and W123's do not. Why MB would do this is anybodys guess as it would be a lifesaver for most people.

From the wiring diagrams, the front fan only comes on with the A/C temp switch on the reciever/dryer.

A thermostat housing neck from a W116 sourced from your local pick-a-part and some "simple" wiring should get you up to speed.

[JMan300sd]

i believe the 82 model is a 126 is it not?

[Larry Delor]

I am assuming you drove from miami to t'hassee on the I-95 & I-10. In other words, you were on the highway most of the time...plenty of airflow.

OK...so the waterpump is new (not rebuilt, but new)...What about the thermostat? I believe they are directional - they must be installed at a certain position.
Fan clutch? Naaw...cuz you have plenty of air flowing through.

Plugged radiatior? A good possibility.

(kinda thinking aloud here)

[autozen]

Make sure the cooling system is completely full which is very tricky on the 126.
Be sure the radiator cap functions properly. This is very important and not a joke. Drive the car, shut the engine down, and immediately feel as much of the back of the radiator as you can with your hand. It should be uncomfortable in all spots. If you feel any cold spots, the radiator is restricted.

Peter

[JMan300sd]

So if the radiator is backed up what should I do? If its the radiator cap should I just replace or can it be adjusted?

[Brian Carlton]

My thought when a W126 had cooling problems on the highway under load is always with the radiator.

Best thing you can do is to remove the radiator from the vehicle and thoroughly clean all the fins.

Now, it takes a good two hours, with the radiator lying flat, to try and blast some cleaning agents and compressed air through all those tiny passages. It's a slow tedious process.

When you first take it out, hold it up to the sun. See all that crap in between the fins? That's blocking the airflow. When you get done with a proper cleaning, at least 75% of that foreign material must be eliminated (preferably all of it, but, I have not figured out how to do it).

These radiators have very narrow passages for air and they are a haven for foreign particles.

You cannot clean this radiator while it is in the vehicle. Don't even waste your time. No improvement will occur.

BTW, if the vehicle gets up to 110°C., it is time to let off on the pedal and drop the boost. Slow the vehicle to 50 and let it cool down.

[tenknots]

I'd go with thermostat next. Radiator after. If it's original, you might as well replace it and not have to worry again. I think they're only $200-250. Someone else can comment if they've ever had one to a radiator shop for rebuilding - I don't know if it can be done to a plastic one.

The more experienced here will tell you to use an infrared thermometer to find out if there are hot/cold spots. Good advice if you have the equipment.

[Rick Miley]

Originally Posted by Larry Delor

Fan clutch? Naaw...cuz you have plenty of air flowing through.

You would think so, but not necessarily. The electric fan relay on my 240D is not reliable, and when it is not working there can be a dramatic rise in temperature, even at highway speeds. The ram air effect is just not as strong as one might expect. So don't dismiss the fan clutch just yet.

[autozen]

I think Tenknots offers good advice about the radiator. You can remove the top hose and check for a metal sleeve in the neck. If you don't see one the radiator is probably original and should be replaced immediately. The original probably has restricted flow, and even if you solve your immediate problem with a thermostat or something else, it will be a waste of time and money, because the neck of that old radiator will break off and if unnoticed will destroy the engine. If you have an old non sleeved radiator it is not a matter of if the neck will break off but a matter of when. I have had it happen twice, but as a professional mechanic I stopped immediately. That, however, is not human nature of the modern American. I cannot count the times that I have been told " I didn't drive it that far. I was only a few miles from home". I always ask the question: " If you were shopping at the mall and a display window broke showering you with shards of glass that severed a main artery causing your heart to pump all your blood out, what would you do? I know that is dramatic to compare a human life to an engine, but in my book $6000.00 is nothing to sneeze at to quote an old axiom.


Peter

[JMan300sd]

Alright...I replaced my thermostat and flushed the system real good with the citric acid flush (there was quite a bit of rust). I put it on the highway for a good two hours and intermittently around town for another 4 and flushed again. Things worked great, it deffinetley stayed below 100. I had a problem though installing the thermostat which is making me hesitant. After replacing it and tightening the bolts I tightened one too much and busted its head off. I would pull out it out with an extractor and replace it with another 10 mil bolt but I dont have one and im driving tomorrow down to miami ( 8 hours). Should I be concerned? I did put quite a bit of gasket sealer and tightened the other bolts very well. And upon arrving in miami i will have access to an extractor and will take care of that promptly, but for the drive is there a possibility that it will cause a serious leak? Thanks again for all the help.

[autozen]

Jman,

Hello, hello. Are you listening or are you in lala land?

Peter

[boneheaddoctor]

Originally Posted by autozen

Jman,

Hello, hello. Are you listening or are you in lala land?

Peter

I agree....the answer is real obvious....YES you do need that bolt. Particularly with an 8 hour drive ahead of you.

[Brian Carlton]

Originally Posted by boneheaddoctor

I agree....the answer is real obvious....YES you do need that bolt. Particularly with an 8 hour drive ahead of you.

I can't remember whether that housing has three bolts on it???

If so, he might be OK. Tough to say with any certainty.

Peter's right, however. The radiator should be replaced.